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  1. #1
    Join Date
    Aug 2016
    Posts
    17

    Default Puzzling Vac problem.

    While we were on board last week we started to experience a very puzzling (well, puzzling to me anyway) problem, that appears to be caused by the Vac "outlets" circuit (ring main). Due to visitors and other commitments I only had time for a quick look for the cause and my plan is to return in a few weeks time and look into it properly and if anyone has any thoughts or ideas, then I would love to hear about them.

    It may have started a few weeks ago, although this could be a red herring, when we returned to our berth after a rough passage when the cockpit took a lot of spray. Upon plugging up to shore power we tripped the supply and the cause appeared to be water in the socket mounted in the cockpit and when it dried out, all was well. Then a couple of days later after some heavy overnight rain, we awoke to find that our supply post had tripped once again and I was able to conclusively confirm that the culprit was once again the cockpit socket and I then replaced it with a new, UK style external double socket.

    All was well until midway through last week when we started to experience an intermittent problem where the "outlet" circuit would trip the supply. This was confirmed by resetting the supply and turning the various circuits back on, one at a time, in no particular order, until the supply tripped and the culprit was always the "outlet" circuit. I say intermittent because some days all was well and others it was not and when it was well, the supply would ALWAYS trip out overnight and that was with absolutely nothing connected to the suspect circuit.

    On Saturday morning I had time for one quick look at the problem and I started at a socket in the mid-berth and while confirming that it was indeed isolated I put a meter across and was surprised to find the following: between both live and neutral and neutral and earth I could measure around 300mVac and between live and earth I measured around 800mVac. I could not measure any shorts between any of the conductors.

    All other circuits --fridge, microwave, battery charger, etc -- continue to operate without any problems and just this loop of cable with 5 sockets connected to it is causing the problem!

    As I say, if anyone has any thoughts before I start pulling the boat to pieces, I would be very pleased to hear from them!

  2. #2
    Join Date
    Sep 2016
    Location
    SoF
    Posts
    9,538

    Default Re: Puzzling Vac problem.

    I know in my boat, after 7000 watts it trips. Perhaps during the night, the fridge compressors etc turn on and overload the circuit
    Neither a Leaver or Remainer be

  3. #3
    Join Date
    Aug 2016
    Posts
    17

    Default Re: Puzzling Vac problem.

    Thanks Bouba for the response, but I don't think that's my problem as when the condition is present the trip will drop-out when the "outlet" circuit is the only circuit on, with nothing at all connected to it.

    Nick.

  4. #4
    Join Date
    Apr 2011
    Location
    Boat- Western Med
    Posts
    5,205

    Default Re: Puzzling Vac problem.

    Unplug the shore power and turn off any inverters .Then open all 5 “ outlets “ and check for dryness and the wiring is ok free from corrosion etc .
    Somehow check for damp at the back of the AC switch panel .
    Go from there .

  5. #5
    Join Date
    Jul 2011
    Posts
    438

    Default Re: Puzzling Vac problem.

    What kind of trip?
    An RCD (Residual current device) is an earth leakage device, it measures the imbalance between live and neutral. An imbalance of (normally) 30ma will trip it as this current has gone to earth.
    An RCBO (residual current circuit breaker with overload) is the same as above with a 30ma leakage current but also act as an overload device eg, 16 a and it will trip

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